Equine Lymphoma Cancer

Q. I am trying to find out if equine lymphoma cancer is hereditary, and any other causes and effects. I had to euthanize my 5-year-old Quarter Horse recently because he had this. How could I have known sooner that he might have had it? Could a purchase exam have detected it? He was never sick a day until this--then in three or four weeks, he was gone. He presented signs that he just wasn't himself, then gradually got worse and worse. I have a 3-year-old nephew to him, and I'm worried about him getting this disease as well.


A. To date, there is no evidence that lymphoma in horses is a heritable disease (nor is it known to be in other species). In other species, cats and cows in particular, it can be caused by a virus, but no evidence has been found to support this mechanism of transmission for this disease in the horse.

Lymphoma is a disease of the lymphoid system where some lymphoid cells become neoplastic (tumorous) and grow in an uncontrolled manner. This results in invasion and disruption of the function of a variety of organs, and causes immune suppression in many affected equine patients. There have been many advances in chemotherapy drugs for this disease in the horse, but at best, the medications might only control the disease for a few months or years.

Unfortunately, there is no surefire way to detect the disease earlier than when some problem occurs that can be clinically detected. Leukemia (an increase in the number of white blood cells in body tissues) is a rare feature of lymphoma in the horse, so routine blood work often will not detect it, and there is no specific blood test available. Most often, this disease occurs in a multicentric (having multiple centers of origin), multiorgan situation and the most common clinical sign is weight loss. Colic, fever, ataxia, or respiratory difficulty can also be seen depending on the particular organ(s) affected.

The prognosis is almost always grave. However, there is a form of lymphoma that occurs only in the skin (cutaneous form); this can wax and wane over several years and might be affected by hormones (regressing under the influence of progesterone). Some think this might just be a precursor to multicentric lymphoma. I am sorry that you lost your horse to this disease, but there is little that you could have done other than having the horse examined by your veterinarian as soon as you detected something amiss.

About the Author

Fairfield Bain, DVM, MS, Dipl. ACVIM, Dipl. ACVP

Fairfield T. Bain, DVM, MS, Dipl. ACVIM, Dipl. ACVP, specializes in internal medicine and pathology. He is an equine technical services veterinarian at Merck Animal Health.

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